Most radar systems in use today are monostatic radar systems, i.e., they are comprised of a single site to perform both a transmitting and a receiving function. Although monostatic radar systems are the most prevalent ones used, they suffer from a drawback in that unable to obtain information which will enable them to determine many important features of targets.
It is well known in the art that a bistatic radar system can overcome the above-defined drawback. However, despite this, bistatic radar has not received wide acceptance in comparison with monostatic radar for the following reasons. First, at least two sites are required for a bistatic system. This is considered to be a drawback for a bistatic system since the cost of additional sites, i.e., the cost of additional personnel, hardware, and supporting facilities, makes a bistatic radar at least twice as expensive as a monostatic radar. Second, in order to process received radar signals effectively in a bistatic system so that maximum information can be obtained, it is necessary to have reference information concerning the original transmitted radar signals. When the separation of two bistatic sites is small, the reference information may be derived from a transmitted signal which is propagated along the earth's surface from the transmitter site to the receiver site, i.e., a direct signal. However, as the separation between the bistatic sites increases, surface attenuation will reduce the strength of the direct signal and degrade its quality. Moreover, whenever there is a large separation between bistatic sites, the direct signal cannot be used to provide the reference information. Although, in an alternative method, the reference information may be obtained by utilizing a stable clock or oscillator, this method suffers in that the use of clocks or oscillators severely restricts the versatility of a bistatic radar system. Third, the volume of observation is limited to an intersection volume of the transmit antenna beam and the received antenna beam. Thus, the use of high-gain antennas by the transmitting and receiving sites leads to inefficient use of the radar power since only the volume common to both beams is used during an observation, i.e., targets outside of the common volume are lost. In order to overcome this drawback, it is known in the prior art to scan the transmitted beam with multiple, simultaneous receiving beams in order to cover a surveillance sector. The use of multiple, simultaneous receiving beams increases the cost and complexity of the bistatic radar system, since the use of multiple, simultaneous receiving beams requires dedicated antennas, receivers, and processors for each receiving beam. In order to reduce the cost of a system using multiple, simultaneous receiving beams, it is known to utilize a pulse chasing method by utilizing a single receiving beam and a single signal processor instead of the multiplicity of receivers and processors used in the multiple, simultaneous receiving beam system. In accordance with the pulse chasing method, the single receiving beam is rapidly scanned over the volume covered by the transmit beam, i.e., to chase the transmit pulse as it propagates away from the transmitting antenna. Since, mechanical beam chasing is impossible, one must use a phase array to chase the transmitted pulse and, this further complicates the problem of resolving volumetric limitation. Fourth, as is well known in the art, synchronization is required between the bistatic transmitting and receiving sites. As the transmitting antenna scans and searches, the receiving antenna must be coordinated so that it can follow and cover the designated scanning and searching volumes. As a result, a command and control link is required to provide such coordination. However, the use of such a command and control link suffers from several drawbacks. A first drawback is that the digital link entails overhead time which occurs as the result of radio frequency (RF) to digital conversion at the receiving site and in digital signal processing of the received radar signal. A second drawback occurs as a result of the need to correct any detected lack of coordination promptly. The correction incurs further overhead in time because such correction requires conversion from analog to digital at the transmitting site as well.
In light of the above, there is a need in the art for a bistatic radar system which is simple and inexpensive and which does not require processing of a received signal at a receiving site.